We aim to understand the basic mechanisms by which loss of any one of three CCM proteins, and specifically of CCM2, leads to the development of Cerebral Cavernous Malformations (CCMs). This in turn should provide potential targets for therapeutic intervention. Our initial approach is focused on understanding the physiologic role of the adaptor protein CCM2 in mice, and the consequences that result from the lack of this gene in mice. CCMs are sporadically acquired or inherited vascular anomalies of the CNS characterized by clusters of dilated thin-walled blood vessels that predispose individuals to seizures and strokes. CCM2 is an adaptor protein for the kinase MEKK3, a MAP3K that can activate MAPK. MEKK3 has also been reported to regulate the activity of the IkappaB Kinase, a kinase complex that activates the NF-kappaB transcription factors downstream of many signals. We originally cloned the genes for both MEKK3 and CCM2. The CCM2 gene was more recently identified as one of three genetic loci mutated in patients with the inherited form of CCM. MAPK signaling pathways have been shown to be essential for cell growth, differentiation and apoptosis. Given the critical contributions of MAPKs and the clinical relevance of CCM2, it is important to fully understand the signaling pathways and targets of the CCM2-MEKK3 signaling module. To explore the in vivo roles of the adaptor protein CCM2 we have generated mice deficient in this protein. The homozygous loss of the adaptor results in early embryonic lethality. In FY 2008 we have determined that this early lethality appears to be due to a block in angiogenesis. With immunohistochemical staining of sections from early embryos we have shown that blood vessel formation ceases starting around day E 8.0. Specifically, these sections fail to stain for markers of arterial cell wells, indicating a block in arterial angiogenesis. In FY 2008 we have also generated conditional knockouts of the CCM2 gene. These mice will be bred to specific deleter strains to determine the cell type that causes early embryonic lethality. One potential cell type that may be affected by loss of CCM2 is the endothelial cell. We have been able to show that silencing of CCM2 in endothelial cells in vitro impaired their proliferation. This is opening up new avenues to understand the physiologic functions of CCM2.